I thought I would share how I use my stereo on the bike.
I find that because of the ride duration, weather, or lighting conditions (day or night) I will wear either a full face, 3/4, or 1/2 helmet. With each helmet I have different stereo needs to make the sound best for the helmet.
I prefer to wear either the 3/4 helmet but sometimes need the 1/2 helmet in high heat for comfort. I wear the full face in cold, wind, night or rain conditions.
On long trips I may go through all of these conditions so I need to be prepared for anything. I used to ride long trips with the bike stereo for music or radio and use my phone on Bluetooth to give me the GPS and phone calls as needed. I now have the USB receiver to play anything the phone can deliver through the bikes stereo. I also have the Bluetooth transmitter and receiver to play the bike or the phone directly to the helmet speakers.
Please let me know if you have options I have not mentioned or better ways of doing what I did mention.
Thanks, Steve